Both for appearance and to maximize air flow to the brakes, automobile wheel styling has tended to emphasize open designs in which the tire-bearing rim is supported on slender spokes or columns connecting the rim to the hub. This is particularly true for alloy (aluminum or magnesium) wheels and is beneficial in reducing wheel mass but results in the imposition of higher stresses than obtain in a wheel designed with a more traditional, generally disc-shaped, spider.
In vehicle use, wheels experience repeated cyclic loads and operate under adverse corrosion conditions. Despite this, wheels are required to exhibit a suitable service lifetime and to achieve this goal current magnesium wheels are forged, primarily to improve their performance under cyclic loading. However magnesium is a difficult material to forge and only a few magnesium alloys are forgeable, which limits the number of magnesium alloys which may be selected. Further it limits the range of wheel designs which may be economically produced, since complex wheel designs cannot be substantially realized by forging alone but they require a combination of forging and extensive machining.
However, tests and simulations demonstrate that wheels are not uniformly stressed but rather experience high stresses only in local regions. This suggests that rather than improving the fatigue performance of the entire wheel, through forging, selective improvement in fatigue performance of a cast magnesium wheel in high stress areas would be equally beneficial in meeting performance goals. Thus a procedure capable of identifying the highly stressed regions and imparting selective fatigue performance improvement would enable the application of reduced cost cast magnesium wheels with performance at least equivalent to that of current forged wheels.